linux文件讀寫文件鎖、select、poll .

一、文件鎖

    文件鎖用於多個用戶共同使用或操作同一個文件。有讀鎖的時候可以再加讀鎖，不能再加寫鎖。有寫鎖的時候，不能加任何鎖，加讀鎖時，該描述符必須是讀打開，加寫鎖時，該描述符必須是寫打開，且只在進程間有用。

重寫的上鎖方法

[cpp] view plain copy print ?

//lock.c
int lock_set(int fd,int type){
    struct flock lock;

    lock.l_type=type;
    lock.l_start=0;
    lock.l_whence=SEEK_SET;
    lock.l_len = 0;
    lock.l_pid=-1;

    fcntl(fd,F_GETLK,&lock);
    if(lock.l_type!=F_UNLCK){
        if(lock.l_type == F_RDLCK)
            printf("Read lock already set by %d!\n",lock.l_pid);
        else if(lock.l_type == F_WRLCK)
            printf("Write lock already set by %d!\n",lock.l_pid);
    }
    lock.l_type = type;
    //此處的F_SETLKW爲F_SETLK的阻塞版本，當無法獲取鎖時進入睡眠等待狀態
    if(fcntl(fd,F_SETLKW,&lock)<0){
        printf("Lock failed:type=%d!\n",lock.l_type);
        exit(1);
    }

    switch(lock.l_type){
        case F_RDLCK:
            printf("read lock set by %d\n",getpid());
            break;
        case F_WRLCK:
            printf("write lock set by %d\n",getpid());
            break;
        case F_UNLCK:
            printf("UN lock set by %d\n",getpid());
            break;
        default:
            break;
    }
}
//lock.c
int lock_set(int fd,int type){
    struct flock lock;

    lock.l_type=type;
    lock.l_start=0;
    lock.l_whence=SEEK_SET;
    lock.l_len = 0;
    lock.l_pid=-1;

    fcntl(fd,F_GETLK,&lock);
    if(lock.l_type!=F_UNLCK){
        if(lock.l_type == F_RDLCK)
            printf("Read lock already set by %d!\n",lock.l_pid);
        else if(lock.l_type == F_WRLCK)
            printf("Write lock already set by %d!\n",lock.l_pid);
    }
    lock.l_type = type;
    //此處的F_SETLKW爲F_SETLK的阻塞版本，當無法獲取鎖時進入睡眠等待狀態
    if(fcntl(fd,F_SETLKW,&lock)<0){
        printf("Lock failed:type=%d!\n",lock.l_type);
        exit(1);
    }

    switch(lock.l_type){
        case F_RDLCK:
            printf("read lock set by %d\n",getpid());
            break;
        case F_WRLCK:
            printf("write lock set by %d\n",getpid());
            break;
        case F_UNLCK:
            printf("UN lock set by %d\n",getpid());
            break;
        default:
            break;
    }
}
上寫鎖

[cpp] view plain copy print ?

#include<stdio.h>
#include<fcntl.h>
#include<unistd.h>
#include"lock.c"

int main(){
    int fd;
    fd=open("readme",O_RDWR|O_CREAT,0666);
    if(fd<0){
        printf("Open file error\n");
        exit(1);
    }
    lock_set(fd,F_WRLCK);
    getchar();
    lock_set(fd,F_UNLCK);
    getchar();
    return 0;

}
#include<stdio.h>
#include<fcntl.h>
#include<unistd.h>
#include"lock.c"

int main(){
    int fd;
    fd=open("readme",O_RDWR|O_CREAT,0666);
    if(fd<0){
        printf("Open file error\n");
        exit(1);
    }
    lock_set(fd,F_WRLCK);
    getchar();
    lock_set(fd,F_UNLCK);
    getchar();
    return 0;

}
上讀鎖

[cpp] view plain copy print ?

#include<stdio.h>
#include<fcntl.h>
#include<unistd.h>
#include"lock.c"

int main(){
    int fd;
    fd=open("readme",O_RDWR|O_CREAT,0666);
    if(fd<0){
        printf("Open file error\n");
        exit(1);
    }
    lock_set(fd,F_RDLCK);
    getchar();
    lock_set(fd,F_UNLCK);
    getchar();
    return 0;

}
#include<stdio.h>
#include<fcntl.h>
#include<unistd.h>
#include"lock.c"

int main(){
    int fd;
    fd=open("readme",O_RDWR|O_CREAT,0666);
    if(fd<0){
        printf("Open file error\n");
        exit(1);
    }
    lock_set(fd,F_RDLCK);
    getchar();
    lock_set(fd,F_UNLCK);
    getchar();
    return 0;

}
在兩個終端中測試：

兩個終端可以同時加上讀鎖。

有一個終端加上讀鎖，則必須等讀鎖釋放才能加寫鎖。

有一個終端加寫鎖必須釋放才能加別的鎖。

二、多路複用：select、poll

[cpp] view plain copy print ?

#include<stdio.h>
#include<fcntl.h>
#include<unistd.h>
#include<memory.h>
#define MAX(a,b) (a>b?a:b)

int main(){
    int fd[3];
    char buff[1024];
    int res,max_fd,i,num;
    fd_set insert,temp_insert;
    struct timeval tv;
    fd[0]=0;
    if((fd[1]=open("in1",O_RDONLY|O_NONBLOCK))<0){
        printf("open in1 error!\n");
        return 1;
    }
    if((fd[2]=open("in2",O_RDONLY|O_NONBLOCK))<0){
        printf("open in2 error!\n");
        return 1;
    }
    //選出最大的fd，select()函數用的
    max_fd=MAX(MAX(fd[0],fd[1]),fd[2]);
    //清空fd_set
    FD_ZERO(&insert);
    for(i=0;i<3;i++){
        FD_SET(fd[i],&insert);
    }
    //設置延遲
    tv.tv_sec=60;
    tv.tv_usec=0;

    while(FD_ISSET(fd[0],&insert) || FD_ISSET(fd[1],&insert) || FD_ISSET(fd[2],&insert)){
        temp_insert = insert;
        //select函數會對fd_set產生修改，只保存變化的文件符，所以要用一個temp
        res=select(max_fd+1,&temp_insert,NULL,NULL,&tv);
        switch(res){
            case -1:
                    printf("select error!\n");
                    return 1;
                    break;
            case 0:
                    printf("time out\n");
                    return 1;
                    break;
            default:
                    for(i=0;i<3;i++){
                        if(FD_ISSET(fd[i],&temp_insert)){
                                memset(buff,0,1024);
                                num=read(fd[i],buff,1024);
                                if(num<0){
                                    return 1;
                                }else if(num == 0){
                                    close(fd[i]);
                                    FD_CLR(fd[i],&insert);
                                }else{
                                    if(i == 0){
                                        if((buff[0] == 'q') || (buff[0] == 'Q')){
                                            return 0;
                                        }
                                    }
                                    write(STDOUT_FILENO,buff,num);

                                }
                        }
                    }
            }
    }
}
#include<stdio.h>
#include<fcntl.h>
#include<unistd.h>
#include<memory.h>
#define MAX(a,b) (a>b?a:b)

int main(){
    int fd[3];
    char buff[1024];
    int res,max_fd,i,num;
    fd_set insert,temp_insert;
    struct timeval tv;
    fd[0]=0;
    if((fd[1]=open("in1",O_RDONLY|O_NONBLOCK))<0){
        printf("open in1 error!\n");
        return 1;
    }
    if((fd[2]=open("in2",O_RDONLY|O_NONBLOCK))<0){
        printf("open in2 error!\n");
        return 1;
    }
    //選出最大的fd，select()函數用的
    max_fd=MAX(MAX(fd[0],fd[1]),fd[2]);
    //清空fd_set
    FD_ZERO(&insert);
    for(i=0;i<3;i++){
        FD_SET(fd[i],&insert);
    }
    //設置延遲
    tv.tv_sec=60;
    tv.tv_usec=0;

    while(FD_ISSET(fd[0],&insert) || FD_ISSET(fd[1],&insert) || FD_ISSET(fd[2],&insert)){
        temp_insert = insert;
        //select函數會對fd_set產生修改，只保存變化的文件符，所以要用一個temp
        res=select(max_fd+1,&temp_insert,NULL,NULL,&tv);
        switch(res){
            case -1:
                    printf("select error!\n");
                    return 1;
                    break;
            case 0:
                    printf("time out\n");
                    return 1;
                    break;
            default:
                    for(i=0;i<3;i++){
                        if(FD_ISSET(fd[i],&temp_insert)){
                                memset(buff,0,1024);
                                num=read(fd[i],buff,1024);
                                if(num<0){
                                    return 1;
                                }else if(num == 0){
                                    close(fd[i]);
                                    FD_CLR(fd[i],&insert);
                                }else{
                                    if(i == 0){
                                        if((buff[0] == 'q') || (buff[0] == 'Q')){
                                            return 0;
                                        }
                                    }
                                    write(STDOUT_FILENO,buff,num);

                                }
                        }
                    }
            }
    }
}

poll用法與select很相似，只是在一些變量上有些不同：

[cpp] view plain copy print ?

#include <unistd.h>
#include <fcntl.h>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <poll.h>

#define MAX_BUFFER_SIZE 1024
#define IO_IN_FILES 3
#define TIME_DELAY 60000

int main() {
    struct pollfd fds[IO_IN_FILES];
    char buff[MAX_BUFFER_SIZE];
    int i,res,real_read;

    fds[0].fd=0;
    if((fds[1].fd=open("in1",O_RDONLY|O_NONBLOCK))<0) {
        printf("Open in1 error!\n");
        return 1;
    }

    if((fds[2].fd=open("in2",O_RDONLY|O_NONBLOCK))<0) {
        printf("Open in2 error!\n");
        return 1;
    }

    for(i=0;i<IO_IN_FILES;i++)
        fds[i].events=POLLIN;

    while(fds[0].events||fds[1].events||fds[2].events) {
        res=poll(fds,IO_IN_FILES,TIME_DELAY);

        switch(res) {
            case -1:
                printf("POLL error!\n");
                return 1;
                break;
            case 0:
                printf("Time out!\n");
                return 1;
                break;
            default:
                for(i=0;i<IO_IN_FILES;i++) {
                    if(fds[i].revents) {
                        memset(buff,0,MAX_BUFFER_SIZE);
                        real_read=read(fds[i].fd,buff,MAX_BUFFER_SIZE);
                        if(real_read<0){
                            printf("Read error!\n");
                            return 1;
                        } else if (real_read==0) {
                            close(fds[i].fd);
                            fds[i].events=0;
                        } else {
                            if (i==0) {
                                if((buff[0]=='q')||(buff[0]=='Q'))
                                    return 0;
                            } else {
                                write(STDOUT_FILENO, buff,real_read);
                            //  buff[real_read]='\0';
                            //  printf("%s",buff);
                            }
                        }

                    }

                }
        }
    }

    return 0;
}

linux文件讀寫文件鎖、select、poll .

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linux文件讀寫文件鎖、select、poll .

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linux文件讀寫 文件鎖、select、poll .

linux文件讀寫文件鎖、select、poll .